Aminoplast curable film-forming compositions providing films having resistance to acid etching

ABSTRACT

An aminoplast-curable film-forming composition is disclosed. The film-forming composition is a crosslinkable composition comprising (1) a material containing a plurality of carbamate and/or urea functional groups and (2) an aminoplast crosslinking agent. The composition provides a coating with improved acid etch resistance, making the coating particularly useful as an automotive clear coat.

This application is a continuation of U.S. Ser. No. 07/968,786 filedOct. 30, 1992, now abandoned.

FIELD OF THE INVENTION

The present invention relates to aminoplast curable film-formingcompositions, and in particular to aminoplast curable compositionsexhibiting superior acid etch resistance.

BACKGROUND OF THE INVENTION

Aminoplast-cured coating systems are well known and provide manyexcellent coating properties. However, it is widely recognized that suchcoatings, particularly clear coats, have poor resistance to etching byacid. Conventional coating systems that contain hydroxyl functionalfilm-forming resins and aminoplast crosslinking agents rely on a curemechanism wherein hydroxyl groups on the resin react with the aminoplastto form ether linkages. See, for example, European Patent Application 0257 848. Although not intending to be bound by any theory, it isbelieved that such ether linkages are vulnerable to acid attack andhence yield coatings with poor acid etch resistance.

Because many geographic areas encounter acidic precipitation, acidresistance in coatings is becoming an increasingly desirable property,particularly for automotive coatings. Hydroxyl-aminoplast coatingsystems of the prior art are not highly effective for providingprotection against etching caused by acid rain.

It is desirable, therefore, to provide a coating system which avoids theproblems of the prior art by demonstrating improved acid etch resistanceproperties.

SUMMARY OF THE INVENTION

In accordance with the present invention, a curable film-formingcomposition is provided, derived from (1) a material containing aplurality of terminal or pendant groups of the structure:

where X is —N or —O and R is H or alkyl of 1 to 18 carbon atoms or R isbonded to X and forms part of a 5 or 6 membered ring and R′ is alkyl of1 to 18 carbon atoms; and (2) an aminoplast crosslinking agentcontaining methylol and/or methylol ether groups. Prior to crosslinking,the film-forming composition comprising the material of (1) and (2) hasa calculated hydroxyl value less than 50 based on solid weight of theclear film-forming composition, excluding any hydroxyl functionalitywhich may be associated with N-methylol groups. The crosslinked coatinghas a substantial number of urethane and/or urea crosslinks that arisefrom reaction of the terminal or pendant groups of structure I or IIwith the aminoplast, thereby providing a high level of acid etchresistance.

DETAILED DESCRIPTION

The film-forming composition is a crosslinkable composition comprising(1) a material containing a plurality of pendant or terminal groups ofthe structure:

where X is —N or —O and R is H or alkyl of 1 to 18, preferably 1 to 6carbon atoms or R is bonded to X and forms part of a five- orsix-membered ring and R′ is alkyl of 1 to 18, preferably 1 to 6 carbonatoms; and (2) an aminoplast crosslinking agent containing methyloland/or methylol ether groups. The material of (1) has on average atleast two pendant or terminal groups of the structure I and/or II,preferably structure I, per molecule. Preferably X=—O. The material of(1) may be an acrylic polymer, a polyester polymer or oligomer, apolyurethane polymer or oligomer, or a blend of two or more of thesematerials. Acrylic polymers are preferred. Prior to crosslinking, thefilm-forming composition of (1) and (2) has a theoretical hydroxyl valueof less than 50, preferably less than 25, and more preferably 0, basedon solid weight of the film-forming composition, excluding any hydroxylfunctionality associated with N-methylol groups such as those in theaminoplast and any hydroxyl functionality which may be associated withN-methylol groups incorporated into the material of (1) such asN-methylol acrylamide groups in the acrylic polymer. By calculatedhydroxyl value is meant the calculated value based on the relativeamounts of the various ingredients used in making the film-formingcomposition, rather than the actual hydroxyl value which is measured onthe film-forming composition itself by conventional techniques. Theresultant crosslinked coating contains a substantial number of urethaneor urea crosslinks that arise from reaction of the terminal or pendantgroups of structure I or II with the aminoplast, thereby providing ahigh level of acid etch resistance.

The acrylic materials are copolymers of one or more alkyl esters ofacrylic acid or methacrylic acid, and, optionally, one or more otherpolymerizable ethylenically unsaturated monomers. Suitable alkyl estersof acrylic or methacrylic acid include methyl methacrylate, ethylmethacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, and2-ethylhexyl acrylate. Suitable other polymerizable ethylenicallyunsaturated monomers include vinyl aromatic compounds such as styreneand vinyl toluene; nitriles such as acrylonitrile and methacrylonitrile;vinyl and vinylidene halides such as vinyl chloride and vinylidenefluoride and vinyl esters such as vinyl acetate; and acid functionalmonomers such as acrylic and methacrylic acid.

Hydroxyl functional monomers such as hydroxyethyl acrylate,hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropylmethacrylate may be copolymerized with the acrylic monomers to imparthydroxyl functionality to the acrylic material in accordance with thetheoretical hydroxyl values mentioned above.

Pendant carbamate functional groups of structure I (X=—O) may beincorporated into the acrylic polymer by copolymerizing the acrylicmonomers with a carbamate functional vinyl monomer, for example acarbamate functional alkyl ester of methacrylic acid. These carbamatefunctional alkyl esters are prepared by reacting, for example, ahydroxyalkyl carbamate, such as the reaction product of ammonia andethylene carbonate or propylene carbonate, with methacrylic anhydride.Other carbamate functional vinyl monomers are, for instance, thereaction product of hydroxyethyl methacrylate, isophorone diisocyanate,and hydroxypropyl carbamate (yielding structure I), or the reactionproduct of hydroxypropyl methacrylate, isophorone diisocyanate, andmethanol (yielding structure II). Still other carbamate functional vinylmonomers may be used, such as the reaction product of isocyanic acid(HNCO) with a hydroxyl functional acrylic or methacrylic monomer such ashydroxyethyl acrylate, and those described in U.S. Pat. No. 3,479,328.Pendant carbamate groups can also be incorporated into the acrylicpolymer by reacting a hydroxyl functional acrylic polymer with a lowmolecular weight alkyl carbamate such as methyl carbamate. Reference ismade to Japanese Kokai 51-4124. Also, hydroxyl functional acrylicpolymers can be reacted with isocyanic acid yielding pendant carbamategroups. Note that the production of isocyanic acid is disclosed in U.S.Pat. No. 4,364,913. Likewise, hydroxyl functional acrylic polymers canbe reacted with urea to give an acrylic polymer with pendant carbamategroups.

Pendant urea groups of structure I (X=—N) may be incorporated into theacrylic polymer by copolymerizing the acrylic monomers with ureafunctional vinyl monomers such as urea functional alkyl esters ofacrylic acid or methacrylic acid. Examples include the condensationproduct of acrylic acid or methacrylic acid with a hydroxyalkyl ethyleneurea such as hydroxyethyl ethylene urea. Other urea functional monomersare, for example, the reaction product of hydroxyethyl methacrylate,isophorone diisocyanate, and hydroxyethyl ethylene urea.

Mixed pendant carbamate and urea groups may also be used.

The acrylic polymer material may be prepared by solution polymerizationtechniques in the presence of suitable catalysts such as organicperoxides or azo compounds, for example, benzoyl peroxide orN,N-azobis(isobutyronitrile). The polymerization may be carried out inan organic solution in which the monomers are soluble by techniquesconventional in the art. Alternately, the acrylic polymer may beprepared by aqueous emulsion or dispersion polymerization techniqueswell known in the art.

The acrylic material typically has a number average molecular weight offrom about 900 to 13,000, preferably from about 1000 to 5000 asdetermined by gel permeation chromatography using a polystyrenestandard, and an equivalent weight of less than 5000, preferably withinthe range of 140 to 2500, based on equivalents of reactive pendant orterminal carbamate or carbamate and/or urea groups. The equivalentweight is a calculated value based on the relative amounts of thevarious ingredients used in making the acrylic material and is based onsolids of the acrylic material.

Polyesters may also be used in the formulation of the film-formingcomposition and may be prepared by the polyesterification of apolycarboxylic acid or anhydride thereof with polyols and/or an epoxide.Usually, the polycarboxylic acids and polyols are aliphatic or aromaticdibasic acids and diols.

The polyols which are usually employed in making the polyester includealkylene glycols, such as ethylene glycol, 1,6-hexanediol, neopentylglycol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionateand other glycols, such as hydrogenated Bisphenol A, cyclohexanediol,cyclohexanedimethanol, caprolactone-based diols, for example, thereaction product of epsilon-caprolactone and ethylene glycol,hydroxy-alkylated bisphenols, polyether glycols, for example,poly(oxytetramethylene) glycol and the like. Polyols of higherfunctionality may also be used. Examples include trimethylolpropane,trimethylolethane, pentaerythritol and the like.

The acid component of the polyester consists primarily of monomericcarboxylic acids or anhydrides thereof having 2 to 18 carbon atoms permolecule. Among the acids which are useful are phthalic acid,isophthalic acid, terephthalic acid, tetrahydrophthalic acid,hexahydrophthalic acid, methyl hexahydrophthalic anhydride, adipic acid,azelaic acid, sebacic acid, maleic acid, glutaric acid, decanoic diacid,dodecanoic diacid and other dicarboxylic acids of various types. Thepolyester may include minor amounts of monobasic acids such as benzoicacid, stearic acid, acetic acid, and oleic acid. Also, there may beemployed higher carboxylic acids such as trimellitic acid andtricarballylic acid. Where acids are referred to above, it is understoodthat anhydrides thereof which exist may be used in place of the acid.Also, lower alkyl esters of the acids such as dimethyl glutarate anddimethyl terephthalate may be used.

Pendant carbamate functional groups of structure I may be incorporatedinto the polyester by first forming a hydroxyalkyl carbamate which canbe reacted with the polyacids and polyols used in forming the polyester.A polyester oligomer may be prepared by reacting a polycarboxylic acidsuch as those mentioned above with a hydroxyalkyl carbamate. An exampleof a hydroxyalkyl carbamate is the reaction product of ammonia andethylene carbonate or propylene carbonate. The hydroxyalkyl carbamate iscondensed with acid functionality on the polyester or polycarboxylicacid, yielding pendant carbamate functionality. Pendant carbamatefunctional groups of structure I may also be incorporated into thepolyester by reacting isocyanic acid or a low molecular weight alkylcarbamate such as methyl carbamate with a hydroxyl functional polyester.Also, pendant carbamate functionality may be incorporated into thepolyester by reacting a hydroxy functional polyester with urea.

Pendant urea groups of structure I may be incorporated into thepolyester by reacting a hydroxyl functional urea such as a hydroxyalkylethylene urea with the polyacids and polyols used in making thepolyester. A polyester oligomer can be prepared by reacting a polyacidwith a hydroxyl functional urea. Also, isocyanate terminatedpolyurethane or polyester prepolymers may be reacted with primaryamines, aminoalkyl ethylene urea, or hydroxyalkyl ethylene urea to yieldmaterials with pendant urea groups. Preparation of these polymers isknown in the art and is described in U.S. Pat. No. 3,563,957.

Mixed pendant carbamate and urea groups may also be used in thepolyester material.

Polyurethanes can be formed by reacting a polyisocyanate with apolyester having hydroxyl functionality and containing the pendantcarbamate and/or urea groups. Alternatively, the polyurethane can beprepared by reacting a polyisocyanate with a polyester polyol and ahydroxyalkyl carbamate or isocyanic acid as separate reactants. Examplesof suitable polyisocyanates are aromatic and aliphatic polyisocyanates,with aliphatic being preferred because of better color and durabilityproperties. Examples of suitable aromatic diisocyanates are4,4′-diphenylmethane diisocyanate, 1,3-phenylene diisocyanate,1,4-phenylene diisocyanate, and toluene diisocyanate. Examples ofsuitable aliphatic diisocyanates are straight chain aliphaticdiisocyanates such as 1,4-tetramethylene diisocyanate and1,6-hexamethylene diisocyanate. Also, cycloaliphatic diisocyanates canbe employed and are preferred because of imparting hardness to theproduct. Examples include 1,4-cyclohexyl diisocyanate, isophoronediisocyanate, alpha,alpha-xylylene diisocyanate and4,4′-methylene-bis-(cyclohexyl isocyanate).

The polyester or polyurethane materials typically have number averagemolecular weights of about 300 to 3000, preferably about 300 to 600 insolvent borne systems and about 900 to 1500 in water borne systems asdetermined by gel permeation chromatography using a polystyrenestandard, and an equivalent weight of from about 140 to 2500 based onequivalents of pendant carbamate and/or urea groups. The equivalentweight is a calculated value based on the relative amounts of thevarious ingredients used in making the polyester or polyurethane and isbased on solids of the material.

Besides polymeric materials, relatively low molecular weight materialscontaining pendant carbamate functional groups of structure II may beformed by reacting isocyanate terminated monomers or oligomers, such asan isocyanurate of polymeric 1,6-hexamethylene dilsocyanate, with analcohol. Any suitable aliphatic, cycloaliphatic, aromatic alkylmonoalcohol or phenolic compound may be used, such as, for example,aliphatic alcohols containing from 1 to 18, preferably lower aliphaticalcohols containing from 1 to 6 carbon atoms such as methanol, ethanol,n-butyl alcohol and n-hexanol; cycloaliphatic alcohols such ascyclohexanol; aromatic-alkyl alcohols such as phenyl carbinol andmethylphenyl carbinol; phenolic compounds such as phenol itself, andsubstituted phenols in which the substituents do not adversely affectcoating operations. Examples include cresol and nitrophenol.

It is possible to prepare blends of the acrylic, polyester, andpolyurethane materials containing pendant or terminal carbamate and/orurea groups described above. It is also possible to prepare blends ofthe low molecular weight materials containing pendant carbamate and/orurea groups with the polymeric materials containing pendant carbamateand/or urea groups. The weight ratio of low molecular weight materialsto polymeric materials may range from 10:90 to 90:10, preferably 10:90to 40:60.

The film-forming composition also includes an aminoplast crosslinkingagent containing methylol and/or methylol ether groups. Aminoplastcondensates are obtained from the reaction of formaldehyde with an amineor amide. The most common amines or amides are melamine, urea, orbenzoguanamine, and are preferred. However, condensates with otheramines or amides can be used; for example, aldehyde condensates ofglycoluril, which give a high melting crystalline product which isuseful in powder coatings. While the aldehyde used is most oftenformaldehyde, other aldehydes such as acetaldehyde, crotonaldehyde, andbenzaldehyde may be used.

The aminoplast contains methylol groups and preferably at least aportion of these groups are etherified with an alcohol to modify thecure response. Any monohydric alcohol may be employed for this purposeincluding methanol, ethanol, butanol, and hexanol.

Preferably, the aminoplasts which are used are melamine-, urea-, orbenzoguanamine-formaldehyde condensates etherified with an alcoholcontaining from 1 to 6 carbon atoms. The aminoplast is present inamounts of about 1 to 80, preferably 10 to 50 percent by weight based onweight of resin solids in the clear film-forming composition. Theequivalent ratio of pendant or terminal carbamate and/or urea functionalgroups of structure I and II above to methylol or methylol ether groupsis 0.5 to 2:1 based on calculated equivalent weights, and beingsufficient to form a crosslinked film.

The film-forming composition may be solvent borne, in which thecarbamate and/or urea functional materials are dissolved in one or morenonreactive organic solvents. Suitable components of the solvent systemwhich may be used are alcohols such as n-propanol and n-butanol, etherssuch as ethylene glycol dibutyl ether and diethylene glycol dibutylether, ketones such as methyl ethyl ketone, methyl isobutyl ketone,methyl amyl ketone and methyl N-butyl ketone; esters such as butylacetate, 2-ethoxyethyl acetate and hexyl acetate; aliphatic andalicyclic hydrocarbons such as the various petroleum naphthas andcyclohexane; and aromatic hydrocarbons such as toluene and xylene. Theamount of solvent used generally can range from about 0 to 55 percent,preferably from about 0 to 50 percent, and most preferably from about 40to 50 percent by weight based on the total weight of the coatingcomposition.

The film-forming composition may also be waterborne. For example,acid-functional materials having terminal or pendant carbamate and/orurea groups may be neutralized with amines and dissolved or dispersed inwater. Also, it is possible to prepare an aqueous dispersion of a blendof acrylic and polyester and/or polyurethane materials with pendantcarbamate and/or urea groups in microparticulate form by a high stresstechnique using a homogenizer. This technique is described in U.S. Pat.No. 5,071,904.

Powder coatings, i.e., film-forming composition is a solid, may also beprepared from the carbamate and/or urea functional materials of thepresent invention. Monomers used to form the carbamate and/or ureafunctional materials are selected such that the resultant material has ahigh glass transition temperature (Tg); that is, greater than 60° C.This material can then be combined with an aldehyde condensate ofglycoluril as mentioned above to form the resinous binder portion of thepowder coating composition. Preferably, the film-forming composition isa liquid.

The film-forming composition will also preferably contain catalysts toaccelerate the cure of the aminoplast and carbamate or urea groups.Examples of suitable catalysts are acidic materials and include sulfonicacids or substituted sulfonic acids such as para-toluenesulfonic acid.The catalyst is usually present in an amount of about 0.5 to 5.0 percentby weight, preferably about 1 to 2 percent by weight, based on weight oftotal resin solids. Optional ingredients such as, for example,plasticizers, flow controllers, anti-oxidants, UV light absorbers andsimilar additives conventional in the art may be included in thecomposition. These ingredients are typically present at up to 25% byweight based on total resin solids.

The composition may be applied to a substrate, or in the case of a clearfilm-forming composition, to a basecoated substrate by any conventionalcoating technique such as brushing, spraying, dipping or flowing, butspray applications are preferred because of superior gloss. Any of theknown spraying techniques may be employed such as compressed airspraying, electrostatic spraying and either manual or automatic methods.

After application of the coating composition, the coated substrate isheated to cure the coating. In the curing operation, solvents are drivenoff and the film-forming material of the coating is crosslinked. Theheating or curing operation is usually carried out at a temperature inthe range of from 160-350° F. (71-177° C.) but if needed, lower orhigher temperatures may be used as necessary to activate crosslinkingmechanisms. The thickness of the coating is usually from about 0.5-5,preferably 1.2-3 mils.

The invention will further be described by reference to the followingexamples. Unless otherwise indicated, all parts are by weight.

EXAMPLES

The following examples (Examples A-N) show the preparation of carbamateand/or urea functional materials and corresponding hydroxyl functionalmaterials.

Example A

A carbamate functional acrylic monomer was prepared from the followingingredients:

Ingredient Weight in Grams isophorone diisocyanate (IPDI) 888.0 dibutyltin dilaurate 4.6 2,6-di-t-butyl methyl phenol 2.6 butyl methacrylate282.0 hydroxypropyl carbamate 571.2 hydroxyethyl methacrylate 416.0

A suitable reactor was charged with the first four ingredients andheated to a temperature of 60° C. The hydroxypropyl carbamate was addedto the reaction mixture over 2 hours. The reaction mixture was then heldat 60° C. until the isocyanate equivalent weight became constant. Thehydroxyethyl methacrylate was then added over 2 hours, and the reactionheld until infrared analysis indicated the absence of isocyanate. Theproduct was diluted with 346.0 g of butyl methacrylate. The finalproduct had a solids content of 75% and had a number average molecularweight of 622 as determined by gel permeation chromatography.

Example B

A low molecular weight, carbamate functional material was prepared fromthe following ingredients:

Ingredient Weight in Grams DESMODUR N-3300¹ 3300.0 dibutyl tin dilaurate4.0 butyl acetate 1592.0 methanol 613.7 ¹Isocyanurate of hexamethylenediisocyanate, available from Miles, Inc.

A suitable reactor was charged with the first three ingredients andheated to a temperature of 60° C. The methanol was added to the reactionmixture over 2 hours. The temperature rose to 74° C. and then was heldat 80° C. until infrared analysis indicated the absence of isocyanate(one and a half hours). The final product had a Gardner-Holdt viscosityof N—O and a number average molecular weight of 961 as determined by gelpermeation chromatography.

Example C

A hydroxyl functional acrylic polymer was prepared from the followingingredients:

Ingredient Weight in Grams hydroxyethyl acrylate 200.0 butylmethacrylate 584.0 α-methyl styrene dimer 16.0 LUPERSOL 555M60¹ 80.0t-butyl perbenzoate 24.0 ¹t-amyl peracetate available from Atochem.

A blend of EKTAPRO EEP (ethyl 3-ethoxypropionate available from EastmanChemicals, 236.8 g) and butyl acetate (105.2 g) was charged to asuitable reactor and heated to reflux. The first three ingredients weremixed with 50 g EKTAPRO EEP. The t-amyl peracetate and 80 g EKTAPRO EEPwere also mixed together. The premixture of acrylic monomers and thepremixture of initiator were added simultaneously to the reaction vesselover a period of about 3 hours while maintaining the reaction at reflux.At the completion of the addition, the reaction mixture was held atreflux for one hour followed by the addition of 8.0 g t-butylperbenzoate over about 30 minutes. The reaction was then held for 30minutes at reflux. 8.0 more grams of t-butyl perbenzoate was added over30 minutes and the reaction held for 30 minutes at reflux. The remainderof t-butyl perbenzoate was added over 30 minutes and the reaction heldat reflux for two hours. An additional total of about 54 grams ofEKTAPR0 EEP was added to the reaction mixture to adjust the solidscontent to about 60%. The reaction mixture was then cooled to roomtemperature. The final product had a solids content of 57% and had anumber average molecular weight of 1220 as determined by gel permeationchromatography. The acrylic polymer had a hydroxyl number of about 92.2based on solids.

Example D

A carbamate functional acrylic polymer was prepared from the followingingredients:

Ingredient Weight in Grams butyl acetate 332.0 EKTAPRO EEP 103.0carbamate functional acrylic monomer 349.9 from Example A butylmethacrylate 279.1 α-methyl styrene dimer 12.5 t-amyl peracetate 63.2butyl acetate 81.4

A suitable reactor was charged with the first two ingredients and heatedto reflux. The carbamate functional acrylic monomer, butyl methacrylateand α-methyl styrene dimer were added to the reaction mixture over 3hours. The t-amyl peracetate and butyl acetate were then added over 3.5hours. The reaction was then held at reflux for one hour, and cooled toroom temperature. The final product had a solids content of 49.9% andhad a number average molecular weight of 1346 as determined by gelpermeation chromatography. The carbamate equivalent weight of theresultant material was approximately 900.

Example E

A carbamate functional acrylic polymer dispersed in aqueous medium wasprepared from the following ingredients:

Ingredient Weight in grams n-propanol 350.0 butyl acrylate 202.0 methylmethacrylate 195.2 carbamate functional acrylic monomer 349.9 fromexample A acrylic acid 25.0 t-dodecyl mercaptan 3.2 t-butyl peroctoate14.4 n-propanol 46.4 dimethyl ethanol amine (DMEA) 23.2 water 700.0

A suitable reactor was charged with the n-propanol and heated to reflux.The next five ingredients were added to the reaction mixture over 3hours. At the same time, the t-butyl peroctoate and 46.4 g n-propanolwere added over 3.5 hours. The reaction was then held at reflux for onehour. The DMEA was added to the reaction mixture at about 95° C.,followed by addition of the water. The reaction cooled to roomtemperature. The final product had a solids content of 35.3% and had anumber average molecular weight of 3728 as determined by gel permeationchromatography. The carbamate equivalent weight of the resultantmaterial was approximately 1040.

Example F

A carbamate functional acrylic latex was prepared from the followingingredients:

Ingredient Weight in Grams Feed A: water 783.4 ALIPAL CO-436¹ 15.1sodium bicarbonate 1.8 Feed B: water 114.8 ammonium persulfate 5.2 FeedC: butyl acrylate 277.5 methyl methacrylate 263.7 carbamate functionalacrylic 502.0 monomer from Example A butyl methacrylate 136.9 acrylicacid 36.4 t-dodecyl mercaptan 18.2 water 757.7 ALIPAL CO-436 17.4DDBSA-DMEA² 11.5 Feed D. diisopropanol amine, 50% in water 67.2 ¹Anionicethoxylated nonyl phenol available from GAF Corporation. ²DDBSA-DMEAsolution was prepared by dissolving 1 mole dodecyl benzene sulfonic acidin water containing 1 mole dimethyl ethanolamine.

A suitable reactor was charged with Feed A and heated to 80° C. 25 g ofFeed C and then all of Feed B were added to the reaction mixture, andthe mixture was held for 20 minutes. The remainder of Feed C was addedover 3 hours. The reaction was held at 80° C. for two hours, and thencooled to room temperature. After dilution with Feed D, the finalproduct had a solids content of 42.8% and had a number average molecularweight of 12,393 as determined by gel permeation chromatography. Thecarbamate equivalent weight of the resultant material was approximately1140.

Example G

A urea functional polyester oligomer was prepared from the followingingredients:

Ingredient Weight in Grams Methylhexahydrophthalic anhydride 840.95hydroxyethylethylene urea¹ 1275.47 butyl stannoic acid 2.12 triphenylphosphite 4.23 xylene 226.1 water 101.7 n-propanol 406.9 ¹Available fromUnion Carbide as UCar RD-65-1.

The first five ingredients were charged to a suitable reactor equippedwith a nitrogen sparge and Dean-Stark trap and heated to reflux. Aswater was removed from the reaction (88.2 g), the acid value of thereaction mixture dropped to less than 5. The reaction mixture was thenvacuum stripped to remove xylene, cooled to 70° C., and diluted with then-propanol and water. The reaction mixture had a final measured solidscontent of 77%, a number average molecular weight of 177 and a weightaverage molecular weight of about 247 as determined by gel permeationchromatography using a polystyrene standard.

Example H

A carbamate functional polyester oligomer was prepared from thefollowing ingredients:

Ingredient Weight in Grams Methylhexahydrophthalic anhydride 505.68ESTERDIOL 204¹ 716.04 butyl stannoic acid 2.12 urea 120 xylene 50n-propanol 1180¹2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate availablefrom Union Carbide.

The first three ingredients were charged to a suitable reactor equippedwith a nitrogen sparge and Dean-Stark trap and heated to reflux. Aswater was removed from the reaction, the acid value of the reactionmixture dropped to less than 1. The reaction mixture was then cooled to150° C., and the urea and xylene were added. The reaction mixture washeld at reflux for 28 hours and then vacuum stripped to remove xylene.After dilution with the n-propanol, the reaction mixture had a finalmeasured solids content of 52.6%, and a viscosity of A on theGardner-Holdt scale.

Example I

A carbamate functional polyester was prepared from the followingingredients:

Ingredient Weight in Grams DOWANOL PM carbamate² 332.5 polyester¹ 455butyl stannoic acid 2.12 ¹Reaction product of hexahydrophthalicanhydride, ESTERDIOL 204, and 1,6-hexanediol in a 1:1:1 mole ratio.²Reaction product of DOWANOL PM and urea, 95% in DOWANOL PM which is themonomethyl ether of propylene glycol and is available from Dow ChemicalCo.

The ingredients were charged to a suitable reactor equipped with anitrogen sparge and Dean-Stark trap and heated to 140-145° C. DOWANOL PMwas removed from the reaction under reduced pressure. The reactionmixture was held until DOWANOL PM carbamate was no longer detectable ona gas chromatograph. The resultant reaction mixture was a soft, waxy,opaque material.

Example J

A pre-emulsion was prepared by stirring together the followingingredients:

Ingredient Weight in Grams carbamate functional polyester 125.0 ofExample I methyl methacrylate 100.0 butyl acrylate 100.0 stearylmethacrylate 25.0 N-methyol acrylamide 83.4 (48% solution in water)methacrylic acid 10.0 dodecylbenzenesulfonic acid (70% in water) 14.3N,N-dimethyl ethanol amine 2.5 IGEPAL CO-897¹ 7.2 ferrous ammoniumsulfate, 1% in water 2.5 water 500.0 ¹Nonionic ethoxylated nonyl phenolavailable from GAF Corp.

The pre-emulsion was passed though an M110 MICROFLUIDIZER high pressureimpingement emulsifier (available from Microfluidics, Inc.) at 8000 psito produce a bluish-white emulsion. The emulsion was transferred to asuitable reactor and blanketed with nitrogen. Polymerization wasinitiated by adding first a mixture of 1.5 g isoascorbic acid and 2.5 gmercaptopropionic acid dissolved in 50.0 g water followed by a solutionof 2.19 g hydrogen peroxide (35%) in 25.0 g water added dropwise over 15minutes. The emulsion exothermed from 26 to 66° C. over 14 minutes. Anyremaining monomer was then polymerized by adding 0.5 g isoascorbic aciddissolved in 5.0 g water followed by 0.5 g of 35% hydrogen peroxide. Anadditional exotherm from 56 to 59° C. was observed. The pH of the latexwas increased to 7.0 with 16.45 g of a 1:1 mixture of water anddiisopropanolamine. The final product had a solids content of 41.0%.

Example K

A urea functional polyester oligomer was prepared from the followingingredients:

Ingredient Weight in Grams dodecanedioic acid 575.0 hydroxyethylethylene urea 637.74 butyl stannoic acid 1.21 xylene 198.66

The ingredients were charged to a suitable reactor and heated to refluxto remove water through a Dean-Stark trap. The temperature of thereaction mixture was held at reflux until the acid value was less than5. The reaction mixture was then cooled to 120° C. and volatilematerials in the reaction mixture were removed under vacuum to a solidscontent of 98.7%. The reaction mixture was diluted to a final solidscontent of 65% with an 80:20 weight mixture of propanol:water. Theproduct had a number average molecular weight of 606 and a ureaequivalent weight of approximately 230.

Example L

A carbamate functional acrylic monomer was prepared from the followingingredients:

Ingredient Weight in Grams hydroxypropyl carbamate 600.0 2,6-di-t-butylmethyl phenol 3.9 triphenyl phosphite 2.22 methacrylic anhydride 810.0toluene 1200.0 sodium hydroxide (16.7%) 1260.0

A suitable reactor was charged with the first four ingredients andheated to 100° C. The reaction mixture was held at this temperatureuntil the methacrylic anhydride had completely reacted with thehydroxypropyl carbamate, as determined by gas chromatography. Thereaction was cooled to room temperature and the toluene and sodiumhydroxide were added. After agitating for about minutes, the reactionmixture was transferred to a separatory funnel. The top layer,containing the product in toluene, was collected in a flask and thetoluene was removed by vacuum distillation.

Example M

A carbamate functional acrylic latex was prepared from the followingingredients:

Ingredient Weight in Grams Feed A. water 450.0 ALIPAL CO-436 9.3 sodiumbicarbonate 0.8 Feed B: water 50.0 ammonium persulfate 2.2 Feed C:carbamate functional acrylic 180.0 monomer of Example L butyl acrylate240.0 methyl methacrylate 120.0 styrene 60.0 acrylic acid 16.8 t-dodecylmercaptan 9.0 water 400.0 ALIPAL CO-436 18.0 PGNP-15¹ 26.0 Feed D:diisopropanol amine, 50% in water 20.0 ¹Nonionic surfactant prepared byreacting 1 mole of nonyl phenol with 15 moles of glycidol.

A suitable reactor was charged with Feed A and heated to 80° C. 25 g ofFeed C and then all of Feed B were added to the reaction mixture, andthe mixture was held for 20 minutes. The remainder of Feed C was addedover 3 hours. The reaction was held at 80° C. for two hours, and thencooled to room temperature. After addition of Feed D, the pH was 7.7.The final product had a solids content of 40.5% and had a number averagemolecular weight of 5706 as determined by gel permeation chromatography.

Example N

A hydroxyl functional acrylic latex was prepared from the followingingredients:

Ingredient Weight in Grams Feed A: water 450.0 ALIPAL CO-436 9.3 sodiumbicarbonate 0.8 Feed B: water 50.0 ammonium persulfate 2.2 Feed C:hydroxyethyl acrylate 180.0 butyl acrylate 240.0 methyl methacrylate120.0 styrene 60.0 acrylic acid 16.8 t-dodecyl mercaptan 9.0 water 400.0ALIPAL CO-436 18.0 PGNP-15 26.0 Feed D: diisopropanol amine, 50% inwater 20.0

A suitable reactor was charged with Feed A and heated to 80° C. 25 g ofFeed C and then all of Feed B were added to the reaction mixture, andthe mixture was held for 20 minutes. The remainder of Feed C was addedover 3 hours. The reaction was held at 80° C. for two hours, and thencooled to room temperature. After addition of Feed D, the pH was 7.84.The final product had a solids content of 40.2% and had a number averagemolecular weight of 5123 as determined by gel permeation chromatography,and a hydroxyl value of 22 based on solids content.

The following examples (1-12) show the preparation of various clearfilm-forming compositions prepared with carbamate, urea, or hydroxylfunctional materials and aminoplast curing agents. The coatingcompositions were evaluated in color-plus-clear applications.

Example 1

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Ingredient Solid weight in grams Solution weight in grams n-butylacetate — 7.0 EKTAPRO EEP — 19.0 TINUVIN 1130¹ 3.0 3.0 TINUVIN 292² 0.30.3 polybutylacrylate³ 0.4 0.7 flow control agent⁴ 1.0 2.3 CYMEL 327⁵30.0 33.3 carbamate containing 69.9 138.8 acrylic of Example D phenylacid phosphate 1.0 1.2 ¹Substituted benzotriazole UV light stabilizeravailable from Ciba Geigy Corporation. ²Sterically hindered tertiaryamine light stabilizer available from Ciba Geigy Corporation. ³A flowcontrol agent having a Mw of about 6700 and Mn of about 2600 made inxylene at 62.5% solids. ⁴Polymeric microparticle prepared in accordancewith example 11 of U.S. Pat. No. 4,147,688. ⁵Highly methylated, highimino content aminoplast resin available from American Cyanamid.

Example 2

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Ingredient Solid weight in grams Solution weight in grams hexyl acetate— 7.0 EKTAPRO EEP — 15.1 TINUVIN 1130 3.0 3.0 TINUVIN 292 0.3 0.3polybutylacrylate 0.4 0.7 flow control agent 1.0 2.3 CYMEL 327 30.0 33.3carbamate containing 49.0 97.0 acrylic of Example D hydroxyl containing20.0 35.1 acrylic of Example C phenyl acid phosphate 1.0 1.2

Example 3

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Ingredient Solid weight in grams Solution weight in grams hexyl acetate— 7.0 EKTAPRO EEP — 18.8 TINUVIN 1130 3.0 3.0 TINUVIN 292 0.3 0.3polybutytacrylate 0.4 0.7 flow control agent 1.0 2.3 CYMEL 327 30.0 33.3carbamate containing 29.0 57.3 acrylic of Example D hydroxyl containing40.0 70.1 acrylic of Example C phenyl acid phosphate 1.0 1.2

Example 4

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Ingredient Solid weight in grams Solution weight in grams hexyl acetate— 7.0 EKTAPRO EEP — 19.3 TINUVIN 1130 3.0 3.0 TINUVIN 292 0.3 0.3polybutylacrylate 0.4 0.7 flow control agent 1.0 2.3 CYMEL 327 30.0 33.3carbamate containing 9.0 17.8 acrylic of Example D hydroxyl containing60.0 105.1 acrylic of Example C phenyl acid phosphate 1.0 1.2

Example 5

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Ingredient Solid weight in grams Solution weight in grams n-butylacetate — 7.0 EKTAPRO EEP — 15.0 TINUVIN 1130 3.0 3.0 TINUVIN 292 0.30.3 polybutylacrylate 0.4 0.7 flow control agent 1.0 2.3 CYMEL 327 30.033.3 hydroxyl containing 69.0 120.7 acrylic of Example C phenyl acidphosphate 1.0 1.2

Example 6

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Solid Ingredient weight in grams Solution weight in grams n-amyl alcohol— 35.1 TINUVIN 1130 3.0 3.0 TINUVIN 292 0.3 0.3 polybutylacrylate 0.40.7 low molecular weight 11.1 15.9 carbamate functional material ofExample B carbamate functional 32.5 64.2 acrylic of Example D ureafunctional 11.1 14.4 polyester of Example G carbamate functional 10.317.3 polyester of Example H phenyl acid phosphate 1.0 1.2

The film-forming compositions of Examples 1-6 were applied to apigmented basecoat to form color-plus-clear composite coatings overelectrocoated steel substrates. The pigmented basecoat for Examples 1-6is commercially available from PPG Industries, Inc. and identified asNHU-9517. The basecoat was pigmented black in color. The electrocoatused on the steel is commercially available from PPG industries, Inc.and is identified as ED-11.

The basecoat was spray applied in two coats to electrocoated steelpanels at a temperature of about 75° F. (24° C.). A ninety second flashtime was allowed between the two basecoat applications. After the secondbasecoat application, a flash time of approximately five minutes wasallowed at 75° F. (24° C.) before the application of the clear coatingcomposition. The clear coating compositions of Examples 1-6 were eachapplied to a basecoated panel in two coats with a ninety second flash at75° F. (24° C.) allowed between coats. The composite coating was allowedto air flash at 75° F. (24° C.) for ten to fifteen minutes before bakingat 285° F. (141° C.) for 30 minutes to cure both the basecoat andclearcoat. The panels were baked in a horizontal position. Theproperties of the composite coatings are reported in Table I below.

TABLE I Hydroxyl % OH Functional Pencil Hardness Exam- Number of Resinby Acid Etch After 3 Minute ple Composition Weight Rating* Xylene Spot**1  0  0 3 F 2 23 20 4 F 3 46 40 5 F 4 69 60 8 F 5 115  100  8 H 6  0  03 H

*Panels were sprayed with a sulfurous acid solution (350 grams deionizedwater and 12 grams sulfurous acid to give a pH of 2.0 plus or minus 0.1)using a polyethylene spray bottle, giving a distribution of drop sizesup to one quarter inch. Approximately 2.5 to 3.0 grams of solution wereapplied per 4×4 inch panel. The panels were then placed in an oven at110° F. (43° C.) for twenty minutes. The panels were removed from theoven and the spray/bake procedure was repeated two more times to give atotal of 60 minutes at 110° F. (43° C.). After the third cycle thepanels were washed with soap and water and dried, then rated for degreeof acid etch resistance on a scale of 1-10 (1=no observable etching;10=severe etching).

**Pencil hardness (Gouge hardness) determined by ASTM D 3353-74 wasperformed immediately after the panel was spotted with a 0.5 inch to 2inch drop of xylene and wiped dry.

Example 7

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Ingredient Solid weight in grams Solution weight in grams TINUVIN 11303.5 3.5 CYMEL 328¹ 30.0 34.9 carbamate containing acrylic of Example E70.0 198.4 phenyl acid phosphate 1.0 5.0 water — 137.0 ¹Waterborneversion of CYMEL 327 available from American Cyanamid.

Example 8

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Ingredient Solid weight in grams Solution weight in grams carbamatecontaining 70.0 162.6 acrylic of Example F CYMEL 303¹ 30.0 30.0 TINUVIN1130 3.5 3.5 DDBSA solution² 1.0 5.0 FC 430 solution³ 0.1 2.0diisopropanol amine — 3.9 solution⁴ n-methyl-2- — 5.0 pyrrolidoneisopropanol — 5.0 water — 25.0 ¹Hexamethoxymethyl melamine resinavailable from American Cyanamid. ²20 weight percent solution ofdodecylbenzene sulfonic acid neutralized with diisopropanolamine indeionized water. ³Nonionic surfactant available from 3M Corporation. ⁴50weight percent solution of diisopropanolamine in deionized water.

Example 9

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Solid weight Solution weight Ingredient in grains in grams DDDA/HEEUoligomer 70.0 116.7 of Example K 30.0 34.9 CYMEL 328 Phenyl acid 1.0 5.0phosphate solution Tego Wet ZFS 453¹ 0.09 0.36 ¹Nonionic surfactantavailable from Tego Chemie Service GmbH.

Example 10

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Solid weight Solution weight Ingredient in grams in grams carbamatefunctional 70.0 170.61 acrylic and polyester latex of Example J CYMEL303 30.0 30.0 TINUVIN 1130 3.5 3.5 DDBSA solution 1.0 5.0 FC 430solution 0.1 2.0 diisopropanol amine solution — 3.2n-methyl-2-pyrrolidone — 5.0 isopropanol — 5.0 water — 58.1

Example 11

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Solid weight Solution weight Ingredient in grams in grams carbamatefunctional 70.0 172.8 acrylic latex of Example M CYMEL 303 30.0 30.0TINUVIN 1130 3.5 3.5 p-TSA solution¹ 1.0 5.0 diisopropanol aminesolution — 3.5 isopropanol — 50.0 water — 17.3 ¹20 weight percentsolution of para-toluene sulfonic acid neutralized with diisopropanolamine in water.

Example 12

A clear film-forming composition was prepared by mixing together thefollowing ingredients:

Solid weight Solution weight Ingredient in grams in grams hydroxylfunctional 70.0 174.2 acrylic latex of Example N CYMEL 303 30.0 30.0TINUVIN 1130 3.5 3.5 p-TSA solution 1.0 5.0 diisopropanol amine solution— 3.5 isopropanol — 50.0 water — 16.3

The film-forming compositions of Examples 7-12 were applied to apigmented basecoat to form color-plus-clear composite coatings overelectrocoated steel substrates. The pigmented basecoat for Examples 7-12is commercially available from PPG Industries, Inc. and identified asBWB-8555. The basecoat was pigmented black in color. The electocoat usedon the steel is commercially available from PPG Industries, Inc. and isidentified as ED-11.

The basecoat was spray applied in two coats to electrocoated steel panelat a temperature of about 75° F. (24° C.) and a relative humidity ofabout 60%. A ninety second flash time was allowed between the twobasecoat applications. After the second basecoat application, a prebaketime of approximately five minutes was allowed at 250° F. (121° C.)before the application of the clear coating composition. The clearcoating compositions of Examples 7-12 were each applied to a basecoatedpanel in two coats with a ninety second flash at 75° F. (24° C.) allowedbetween coats. The composite coating was allowed to air flash at 75° F.(24° C.) for ten to fifteen minutes and to flash at 140° F. (60° C.) forten to fifteen minutes before baking at 285° F. (141° C.) for 30 minutesto cure both the basecoat and clearcoat. The panels were baked in ahorizontal position. The properties of the composite coatings arereported in Table II below.

TABLE II Example Acid Etch Rating  7 3  8 3  9 2 10 5 11 5 12 9

We claim:
 1. A curable film-forming composition comprising (1) 50 to 90percent by weight based on weight of resin solids in the film-formingcomposition of a material selected from the group consisting ofpolyesters, polyurethanes formed from polyisocyanates, or mixturesthereof and containing a plurality of terminal or pendant urea orcarbamate groups only of the structure:

where X is

or —O and R is H or alkyl of 1-6 carbon atoms or R is bonded to X andforms part of a 5 or 6 membered ring; and (2) 10 to 50 percent by weightbased on weight of resin solids in the film-forming composition of anaminoplast crosslinking agent containing methylol and/or methylol ethergroups; said film-forming composition being crosslinkable throughreaction of said pendant or terminal groups with said methylol and/ormethylol ether groups wherein the equivalent ratio of said pendant orterminal groups to methylol ether groups is from 0.5 to 2:1 and issufficient to form a crosslinked film; said film-forming compositionbeing further characterized as having a calculated hydroxyl value lessthan 50 based on solid weight of said film-forming composition,excluding any hydroxyl functionality associated with N-methylol groupsof the aminoplast crosslinking agent so as to result in a crosslinkedcoating which has a substantial number of urethane crosslinks arisingfrom said reaction of pendant or terminal groups with said methyloland/or methylol ether groups, giving said crosslinked coating a highlevel of acid etch resistance.
 2. The composition of claim 1 in whichthe material has on average at least two of said terminal or pendantgroups per molecule.
 3. The composition of claim 1 in which the materialhas an equivalent weight of from about 140 to 2500 based on equivalentsof said terminal or pendant groups.
 4. The composition of claim 1 inwhich R is H.
 5. The composition of claim 1 in which the aminoplast is acondensate of melamine with formaldehyde and optionally an alcoholcontaining from 1 to 6 carbon atoms.
 6. A curable film-formingcomposition comprising (1) 50 to 90 percent by weight based on weight ofresin solids of a polymer or oligomer containing a plurality of terminalor pendant urea groups of the structure:

where X is

and R is H or alkyl of 1-6 carbon atoms or R is bonded to X and formspart of a 5 or 6 membered ring; and (2) 10 to 50 percent by weight basedon weight of resin solids of an aminoplast crosslinking agent containingmethylol and/or methylol ether groups; said clear film-formingcomposition being crosslinkable through reaction of said pendant orterminal groups with said methylol and/or methylol ether groups; saidclear film-forming composition being further characterized as having acalculated hydroxyl value less than 50 based on solid weight of saidclear film-forming composition, excluding any hydroxyl functionalityassociated with N-methylol groups so as to result in a crosslinkedcoating which has a substantial number of urea crosslinks arising fromsaid reaction of pendant or terminal groups with said methylol and/ormethylol ether groups, giving said crosslinked coating a high level ofacid etch resistance.
 7. The composition of claim 1 in which (1) is anacrylic polymer.
 8. The composition of claim 7 in which the acrylicpolymer has an equivalent weight less than 5000 based on equivalents ofsaid terminal or pendant groups.
 9. The composition of claim 8 in whichthe acrylic polymer has an equivalent weight within the range of about140 to 2500 based on equivalents of said terminal or pendant groups. 10.The composition of claim 6 in which (1) is a polymer selected from thegroup consisting of polyesters, polyurethanes, or mixtures thereof. 11.The composition of claim 10 in which the polymer has on average at leasttwo of said terminal or pendant groups per molecule.
 12. The compositionof claim 11 in which the polymer has an equivalent weight of from about140 to 2500 based on equivalents of said terminal or pendant groups. 13.The composition of claim 6 in which R is H.
 14. The composition of claim6 in which the aminoplast is a condensate of melamine with formaldehydeand optionally an alcohol containing from 1 to 6 carbon atoms.
 15. Thecomposition of claim 6 wherein the equivalent ratio of said pendant orterminal groups to methylol or methylol ether groups is from 0.5 to 2:1and is sufficient to form a crosslinked film.
 16. A curable coatingcomposition comprising: (A) a carbamate-functional polymer that is thereaction product of a mixture comprising: (1) a polymer that is thereaction product of a mixture comprising: (a) a polyisocyanate and (b)an active hydrogen-containing chain extension agent, and (2) a compoundhaving a group that is reactive with said polymer (A)(1) and a carbamategroup or group that can be converted to carbamate, and (B) a compoundhaving a plurality of functional groups that are reactive with carbamategroups on said carbamate-functional polymer.
 17. A curable coatingcomposition according to claim 16 wherein the polymer (A)(1) isterminated with isocyanate groups, and the compound (A)(2) has a groupthat is reactive with isocyanate and a carbamate group or group that canbe converted to carbamate.
 18. A curable coating composition accordingto claim 17 wherein the compound (A)(2) is a carbamate compound havingan active hydrogen group.
 19. A curable coating composition according toclaim 18 wherein the compound (A)(2) is a hydroxyalkyl carbamate.
 20. Acurable coating composition according to claim 16 wherein the polymer(A)(1) has a number average molecular weight of about 300 to
 3000. 21. Acurable coating composition according to claim 16 wherein the polymer(A)(1) is a polyurethane that is the reaction product of apolyisocyanate and a polyol.
 22. A curable coating composition accordingto claim 16 wherein the compound (B) is an aminoplast.
 23. A curablecoating composition according to claim 22 wherein the aminoplast is amelamine formaldehyde resin.
 24. A curable coating composition accordingto claim 22 wherein the aminoplast is a urea formaldehyde resin.
 25. Acolor-plus-clear composite coating wherein the clear coating is derivedfrom a curable coating composition according to any of claims 16-24. 26.A curable composition comprising: (A) a carbamate-functional polymerthat is the reaction product of a mixture comprising: (1) a polymer thatis the reaction product of a mixture comprising: (a) a polyisocyanateand (b) an active hydrogen-containing chain extension agent and (2) acompound having a group that is reactive with said polyurethane and acarbamate group or group that can be converted to carbamate, and (B) acompound having a plurality of functional groups that are reactive withcarbamate groups on said carbamate-functional polymer.
 27. A curablecoating composition comprising: (A) a carbamate-functional polyurethanepolymer formed from materials comprising (1) a polyisocyanate, (2) apolyol, and (3) a compound that is reactive with isocyanate or hydroxyland contains or is convertible to carbamate; and (B) a compound having aplurality of functional groups that are reactive with carbamate on saidcarbamate-functional polymer.
 28. A curable coating composition as setforth in claim 27, wherein said coating composition is furthercharacterized as having a calculated hydroxyl value less than 50 basedon solid weight of said coating composition, excluding any hydroxylfunctionality associated with said compound (B).
 29. A curablefilm-forming composition comprising (1) 50 to 90 percent by weight basedon weight of resin solids in the film-forming composition of apolyurethane formed from polyisocyanates, and containing a plurality ofterminal or pendant carbamate groups of the structure:

where R is H or alkyl of 1-6 carbon atoms; and (2) 10 to 50 percent byweight based on weight of resin solids in the film-forming compositionof an aminoplast crosslinking agent containing methylol and/or methylolether groups; said film-forming composition being crosslinkable throughreaction of said pendant or terminal groups with said methylol and/ormethylol ether groups, wherein the equivalent ratio of said pendant orterminal groups to methylol ether groups is from 0.5 to 2:1 and issufficient to form a crosslinked film; said film-forming compositionbeing further characterized as having a calculated hydroxyl value lessthan 50 based on solid weight of said film-forming composition,excluding any hydroxyl functionality associated with N-methylol groupsof the aminoplast crosslinking agent so as to result in a crosslinkedcoating which has a substantial number of urethane crosslinks arisingfrom said reaction of pendant or terminal groups with said methyloland/or methylol ether groups, giving said crosslinked coating a highlevel of acid etch resistance.
 30. A curable coating compositioncomprising: (A) a carbamate functional polymer that is the reactionproduct of a mixture comprising; (1) a polymer that is the reactionproduct of a mixture comprising: (a) a polyisocyanate and (b) a polyolactive hydrogen-containing chain extension agent, and (2) a compoundthat is reactive with isocyanate or hydroxyl of said polymer(A) (1) andcontains or is convertible to carbamate; and (B) an aminoplastcrosslinking agent containing methylol and/or methylol ether groups,reactive with carbamate groups on said carbamate functional polymer (A).31. A curable coating composition as set forth in claim 30 being furthercharacterized as having a calculated hydroxyl value less than 50 basedon solid weight of said coating composition, excluding any hydroxylfunctionality associated with N-methylol groups of the aminoplastcrosslinking agent.
 32. A curable coating composition as set forth inclaim 31 wherein said polyol (A) (1) (b) is a polyester polyol.